Unusually high concentrations of magnetite at Caraiba and other Cu-sulfide deposits in the Curaca Valley, Bahia, Brazil

The Curaça Valley, in Bahia, Brazil, contains several pyroxenite-hosted Cu-sulfide deposits. They have unusually high Cu and low Ni contents (Cu/Ni up to 2500), with chalcopyrite and bornite being the dominant sulfides (Cu/S up to 3.5). Oxides (magnetite and lesser ilmenite) constitute approximately 50% of the opaque phases. Most other magmatic Cu-Ni-sulfide deposits contain between 2 and 15% oxides. The only other known magmatic sulfide deposits with comparable Cu/Ni values, at Okiep, South Africa. also have elevated contents of magnetite. There, the oxides have been interpreted as a result of oxidation and desulfurization of primary sulfides, resulting in a high abundance of pure magnetite. In the Curaça Valley, reaction-replacement of sulfides to form magnetite is not apparent: the magnetite contains up to 14 wt% Cr₂0₃, 2% V₂0₃, 7% Ti0₂, and 1% ZnO, and is generally replaced by chalcopyrite and bomite. However, the composition of the oxides seems to have been modified by equilibration with associated orthopyroxene, in response to high-grade metamorphism. The metamorphism could also have led to significant S-loss of the sulfides, reflected by relatively low S/Se values of the rocks (200-1500). As at Okiep, a large proportion of the oxides secms lo have becn a product of replacement of primary sulfides. La vallée de Curaça. dans l'état de Bahia, au Brésil, contient plusieurs gisements de sulfures de cuivre dans un hôte pyroxénitique. Le minerai est fortement enrichi en Cu et remarquablement appauvri en Ni (le rapport Cu/Ni atteignant 2500); chalcopyrite et bornite sont les sulfures dominants (Cu/S jusqu'à 3.5). Les oxydes (magnétite surtout, avec ilménite accessoire) constituent environ 50% des phases opaques. La plupart des autres gisements de sulfures de Cu-Ni contiennent entre 2 et 15% d'oxydes. Les seuls gisements de sulfures magmatiques connus ayant une valeur Cu/Ni comparable se trouvent à Okiep, en Afrique du Sud; ils sont aussi enrichis en magnétite. Dans ce cas, on a interprété la proportion élevée en magnétite pure en termes d'oxydation et de perte de soufre des sulfures primaires. Dans la vallée de Curaça, un remplacement des sulfures par la magnétite ne semble pas évident. La magnétite contient jusqu'à 14% (poids) de Cr₂0₃, 2% de V₂0₃, 7% de Ti0₂ et 1% de ZnO, et semble plutôt remplacé par la chalcopyrite et la bomite. Toutefois, la composition des oxydes semble avoir été modifiée par équilibrage avec l'orthopyroxène associé, en réponse à un métamorphisme de forte intensité. Cet épisode de métamorphisme aurait pu déstabiliser les sulfures et causer une perte en soufre, comme l'indique le faible rapport S/Se des roches (200-1500). Tout comme à Okiep. une proportion importante des oxydes semble s'être formée par remplacement des sulfures primaires

Nudging towards a healthier life? Conceptualising the role of health apps and wearables between empowerment and manipulation

"What once has been thought, cannot be taken back." (Friedrich Dürrenmatt, The Physicists) In Dürrenmatts play, the physicist Möbius has discovered the world formula and is afraid of its destructive potential, which poses a threat to global security. In order to ensure that his dismal discovery will not become harmful, he checks into a lunatic asylum. Tragically, his plan fails and his discovery falls into the wrong hands, which leads him to resignation and to the above-quoted insight. The lesson to be drawn from this play is that technological innovations have a huge influence on individual and social behaviour and that we cannot stop new technology from being used. However, we have the possibility to establish forms of public governance, ensuring that innovation works for the individual and common good. Health apps and wearables may appear to be a comparatively minor innovation, but they have the potential to change our society significantly, and the widespread use of this technology reminds us that it is high-time to analyse its potential, ranging from empowerment to the manipulation of users

How do Pedagogical Conversational Agents affect Learning Outcomes among High School Pupils: Insights from a Field Experiment

Pedagogical conversational agents (CA) support formal and informal learning to help students achieve better learning outcomes by providing information, guidance or fostering reflections. Even though the extant literature suggests that pedagogical CAs can improve learning outcomes, there exists little empirical evidence of what design features drive this effect. This study reports on an exploratory field experiment involving 31 pupils in commercial high schools and finds that students achieved better learning outcomes when preparing for their tests with a pedagogical CA than without. However, the drivers of this effect remain unclear. Neither the use frequency of the design features nor the pupils’ expectations towards the CA could explain the improvement in marks. However, for the subjective perception of learning achievement, pupils’ expectations was a significant predictor. These findings provide support for the use of pedagogical CAs in teaching but also highlight that the drivers of better learning outcomes still remain unknown

Exploration for magmatic Ni-Cu-PGE sulphide deposits : a review of recent advances in the use of geochemical tools, and their application to some South African ores

Most major magmatic Cu-Ni-PGE sulphide deposits are thought to have formed by segregation of an immiscible sulphide melt from a silicate host magma, in response to processes such as magma mixing, rapid cooling, differentiation, and contamination. The metal content of the sulphides is governed by the concentration of the metals in the silicate host magma, the sulphide melt/silicate melt partition coefficients (D values) of the metals, and the R-factor during sulphide segregation. Fractionation between the metals occurs during partial melting of the upper mantle source, crystallization of oxides, platinum-group minerals (PGM), and silicates (mainly olivine and less so orthopyroxene), segregation of sulphide melt, and crystallization of the sulphide melt. The latter process may yield zoned ore bodies consisting of Os, Ir, Ru, Rh, Fe, (Ni)-rich monosulphide solid solution (mss) cumulate ore and fractionated sulphide ore rich in Cu, Pt, and Pd. It is possible to model these processes and thereby to estimate the potential of a magmatic body to host economic Cu-Ni-PGE sulphide deposits. The location of Cu-Ni-PGE sulphide ores may be facilitated by applying a number of geochemical tools. PGE-rich horizons within layered intrusions are particularly difficult to locate because the ore zones are generally thin compared to the thickness of the intrusions. Variation in Cu/Pd ratios of the silicate rocks may delineate the position of some of these horizons, since the strongly chalcophile Pd is preferentially depleted during sulphide segregation, resulting in an increase in Cu/Pd of the subsequently crystallizing overlying cumulates. Cu/Pd ratios may also be applied in sill-like bodies such as the Uitkomst intrusion, Mpumalanga, to estimate the potential for conduit-type deposits, and in lavas where they may help to locate possible Noril'sk-type mineralized feeder zones to basalt flows. Other methods of determining whether igneous bodies have experienced magma mixing and sulphide segregation are based on Ni contents of olivines, Ti contents, and Cr/Fe ratios of spinels, and petrographic features such as the presence of plagioclase inclusions within ferromagnesian phases. Se/S ratios may help to determine whether magmatic sulphide ores underwent post-magmatic (metamorphic or hydrothermal) sulphur loss. They may also discriminate between a magmatic or sedimentary source of the S, and between a magmatic or hydrothermal origin of the metals. Hydrothermal sulphide ores may further be distinguished from magmatic ores by means of significantly higher Cu/Ni and Pd/Ir ratios of the former. Such distinction is important because it would be futile to investigate hydrothermal deposits for magmatic ore zonation

Platinum-group element contents of Karelian kimberlites: implications for the PGE budget of the sub-continental lithospheric mantle

We present high-precision isotope dilution data for Os, Ir, Ru, Pt, Pd and Re in Group I and Group II kimberlites from the Karelian craton, as well as 2 samples of the Premier Group I kimberlite pipe from the Kaapvaal craton. The samples have, on average, 1.38 ppb Pt and 1.33 ppb Pd, with Pt/Pd around unity. These PGE levels are markedly lower, by as much as 80%, than those reported previously for kimberlites from South Africa, Brazil and India, but overlap with PGE results reported recently from Canadian kimberlites. Primitive-mantle-normalised chalcophile element patterns are relatively flat from Os to Pt, but Cu, Ni and, somewhat less so, Au are enriched relative to the PGE (e.g., Cu/Pd > 25.000). Pd/Ir ratios are 3,6 on average, lower than in most other mantle melts. The PGE systematics can be largely explained by two components, (i) harzburgite/lherzolite detritus of the SCLM with relatively high IPGE (Os-Ir-Ru)/PPGE (Rh-Pt-Pd) ratios, and (ii) a melt component that has high PPGE/IPGE ratios. By using the concentrations of iridium in the kimberlites as a proxy for the proportion of mantle detritus in the magma, we estimate that the analysed kimberlites contain 3–27% entrained and partially dissolved detritus from the sub-continental lithospheric mantle, consistent with previous estimates of kimberlites elsewhere (Tappe S. et al., 2016, Chem. Geol. http://dx.doi.org/10.1016/j.chemgeo.2016.08.019). The other major component in the samples is melt, modelled to contain an average of 0.85 ppb Pt and 1.09 ppb Pd. Assuming that Group II kimberlites are derived from relatively metasomatised SCLM, our data suggest that the metasomatised Karelian SCLM is relatively poor in Pt and Pd. If our data are representative of other Group II kimberlites elsewhere, this result could imply that the PGE enrichment in certain continental large igneous provinces, including Bushveld, is not derived from melting of metasomatised SCLM

Petrogenesis of Cu-Ni sulphide ores from O’okiep and kliprand, Namaqualand, South Africa : constraints from chalcophile metal contents

The petrogenesis of sulphide ores in the O’okiep district has remained controversial. Based mainly on the concentration of chalcophile metals (PGE, Cu, Ni), it is proposed that the sulphides segregated from a basaltic magma generated during melting of sub-continental lithospheric mantle. Sulphide saturation of the magma was delayed due to relatively high fO2 until crustal contamination occurred during the advanced stages of differentiation. The immiscible sulphide melt was entrained and fractionated in dynamic magma conduits. Sulphides enriched in monosulphide solid solution (mss) component precipitated at depth in the Kliprand area of southern Namaqualand to form the Hondekloof deposits, whereas the O’okiep ores crystallised at shallower levels from highly fractionated residual sulphide liquids enriched in intermediate solid solution (iss). Sulphides of intermediate composition occur at Ezelsfontein. In the context of this model, the O’okiep intrusions could represent the proximal magmatic members of an IOCG suite of deposits, raising the prospect for additional IOCG deposits elsewhere in southern Africa. The model also predicts an enhanced potential at O’okiep for undiscovered Ni sulphide ores at depth

Protective effects of polyamine depletion in mouse models of type 1 diabetes: implications for therapy

The underlying pathophysiology of type 1 diabetes involves autoimmune-mediated islet inflammation, leading to dysfunction and death of insulin-secreting islet β cells. Recent studies have shown that polyamines, which are essential for mRNA translation, cellular replication, and the formation of the hypusine modification of eIF5A may play an important role in the progression of cellular inflammation. To test a role for polyamines in type 1 diabetes pathogenesis, we administered the ornithine decarboxylase inhibitor difluoromethylornithine to two mouse models--the low-dose streptozotocin model and the NOD model--to deplete intracellular polyamines, and administered streptozotocin to a third model, which was haploinsufficient for the gene encoding the hypusination enzyme deoxyhypusine synthase. Subsequent development of diabetes and/or glucose intolerance was monitored. In the low-dose streptozotocin mouse model, continuous difluoromethylornithine administration dose-dependently reduced the incidence of hyperglycemia and led to the preservation of β cell area, whereas in the NOD mouse model of autoimmune diabetes difluoromethylornithine reduced diabetes incidence by 50%, preserved β cell area and insulin secretion, led to reductions in both islet inflammation and potentially diabetogenic Th17 cells in pancreatic lymph nodes. Difluoromethylornithine treatment reduced hypusinated eIF5A levels in both immune cells and islets. Animals haploinsufficient for the gene encoding deoxyhypusine synthase were partially protected from hyperglycemia induced by streptozotocin. Collectively, these studies suggest that interventions that interfere with polyamine biosynthesis and/or eIF5A hypusination may represent viable approaches in the treatment of diabetes

Compositional variation of laurite at Union Section in the Western Bushveld Complex

One hundred and forty five grains of laurite in polished sections of samples from one borehole through the major chromitite layers and some chromite-bearing silicate rocks of the Lower and Critical Zones of the western Bushveld Complex at Union Section have been located and analysed by scanning electron microscope. Ninety per cent by number of laurite grains are included within chromite, with the remainder being located on chromite-silicate grain boundaries, and in interstitial silicates and sulphides. The composition of laurite shows considerable variation within individual samples. Furthermore, there is no apparent correlation between whole-rock Ru and Cr contents in our samples, arguing against a model whereby laurite exsolved from the chromite lattice. Based on a well-defined correlation between whole-rock S, PPGE (Rh+Pt+Pd), and IPGE (Os+Ir+Ru) contents, we favour a mechanism whereby laurite crystallized from segregating sulphide melt and was subsequently entrapped by growing chromite grains